Self-piercing and clinching fastener have been used for many years in mass production applications, particularly by the automotive industry, to attach components, for example, to structural elements. Such self-attaching fasteners normally include a body portion and a projecting fastening portion. The installation apparatus includes an installation head having a reciprocating plunger and a die member or die button which rigidly supports the plate or panel to which the self-attaching fastener is to be installed. In a typical mass production application, the installation head and die button are installed in the opposed die platens of a die press which may simultaneously form the plate or panel into a contoured shape. Several self-attaching fasteners may be installed in the plate or panel with each stroke of the die press.
The body portion of the self-attaching fastener is supported in the reciprocating plunger of the installation head and the fastening portion extends axially from the plunger. When the die press is reciprocated to close the press, the plunger of the installation head drives the fastener into the panel. Where the fastener is a self-piercing fastener having a pilot or barrel portion, the fastener pierces a slug from the panel and the pilot or barrel portion is then received through the pierced panel opening. Such fasteners may also be installed in panels having a preformed panel opening. The die button then deforms the panel adjacent the panel opening into locking engagement with the fastener. Examples of pierce nuts and installation tooling are disclosed in U.S. Pat. Nos. 3,152,628, 3,648,747, 3,711,931, 4,242,793 and 4,971,499, all assigned to the assignee of the present application.
More recently, self-attaching stud and nut fasteners have been developed and commercialized having an annular barrel portion which projects from the body portion of the fastener. The barrel portion performs a similar function to the pilot portion of the pierce and clinch nuts described in the above-referenced U.S. patents; however the barrel portion of the fastener is deformed radially outwardly simultaneously with the deformation of the panel to form a very secure mechanical interlock between the fastener and the panel. U.S. Pat. Nos. 4,711,021, 4,713,872, 4,915,558 and 4,831,698 disclose typical examples of such self-attaching studs and nuts and commercial embodiments of the installation tooling.
The installation tooling for such self-attaching fasteners, however, places certain limitations upon the use of such fasteners. Where the installation head is attached to the upper die shoe in a "down pierce" arrangement, the panel and die button are rigidly supported in the lower die shoe. In an "up pierce" arrangement, the pierce nut must be rigidly supported in the lower die shoe and the die button is in the upper platen. Thus, it is not possible to install a self-attaching fastener of the type described above in a tube or enclosed structure, particularly from inside the structure. The tube will collapse under the force of the installation unless the wall to which the fastener is being attached and die button are rigidly supported. However, structural metal tubes are now used in many applications, including automotive applications, requiring attachment of components and other structural members to the structural metal tubes. The thickness of the wall of the metal tube may be 1/8 inch or greater. In many applications, the structural tube is preferably flattened at the point of connection. Thus, attachment of a component to a structural metal tube may require flattening of the tube at the point of connection, then welding a weld nut to the flattened area, or use of a clamp. The method and apparatus of the present invention is particularly suitable for attaching self-attaching nuts of the type described above to structural metal tubes or the metal wall of an enclosed structure, from inside the tube or structure. The self-attaching fastener may be installed with one stroke of the press and the area surrounding the fastener is simultaneously flattened to form a cradle or saddle for attachment of a second structural element or component. Thus, the method and apparatus of this invention solves a difficult problem associated with prior methods and apparatus, permitting the use of conventional self-attaching fasteners in enclosed structures, such as structural tubes.